On Fri, Feb 21, 2020 at 12:46 AM Magnus Karlsson <magnus.karlsson@xxxxxxxxx> wrote: > > On Fri, Feb 21, 2020 at 9:40 AM Eelco Chaudron <echaudro@xxxxxxxxxx> wrote: > > > > > > > > On 21 Feb 2020, at 9:33, Magnus Karlsson wrote: > > > > > On Fri, Feb 21, 2020 at 9:30 AM Eelco Chaudron <echaudro@xxxxxxxxxx> > > > wrote: > > >> > > >> > > >> > > >> On 20 Feb 2020, at 23:49, William Tu wrote: > > >> > > >>> Hi, > > >>> > > >>> I'm trying to save some CPU cycles when there is no packet arrives. > > >>> I enable the poll syscall option of xdpsock, by doing > > >>> > > >>> $ ./xdpsock -r -p -S -i ens16 > > >>> sock0@ens160:0 rxdrop xdp-skb poll() > > >>> pps pkts 1.00 > > >>> rx 0 0 > > >>> tx 0 0 > > >>> > > >>> Since there is no packet coming, I though by calling poll() > > >>> system call, the xdpsock process will be blocked and CPU utilization > > >>> should be way under 100%. However, I'm still seeing 100% > > >>> CPU utilization. Am I understanding this correctly? > > >> > > >> Hi William, I can remember I saw this in the past two with this code. > > >> It > > >> had something to do with the way xdpsock waits for the buffers to be > > >> free’ ed by the kernel. What I can remember it had something to do > > >> with the veth interfaces also. > > >> > > >> I do remember that I fixed it in the tutorial for AF_XDP: > > >> https://github.com/xdp-project/xdp-tutorial/blob/master/advanced03-AF_XDP/af_xdp_user.c > > > > > > Eelco, > > > > > > Do you remember exactly what you had to fix in the xdpsock sample? > > > Your tutorial is quite a rewrite so it is hard for me to tell exactly > > > which of all the changes that fix this problem. The reason I ask is > > > that it would be nice to fix this in the sample too. > > > > > > Thanks: Magnus > > > > From an earlier email conversation we had this is where it looped in my > > case: > > Thanks Eelco. Yes, the xdpsock sample is too simplistic in this case. > I will put this on my backlog to fix so that we do not have this > problem in the future. I might take some inspiration from your code > :-). Hope you do not mind. > > /Magnus > Hi Magnus and Eelco, Thanks for your reply. I run Eelco's af_xdp_user.c and indeed, with poll syscall, the CPU is way under 100%. But I'm still figuring out the difference and where to fix in xdpsock_user.c. Regards, William
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